In this description, a bioactive material refers to a material designed to induce specific biological activity in a body tissue. Bioactive glass refers to any glass that displays characteristics of bioactivity. Bioactive glass is an amorphous solid that is not intrinsically adhesive and that is capable of forming a cohesive bond with both hard and soft tissue when exposed to appropriate in vivo and in vitro environments, such as simulated body fluid or tris-hydroxymethylaminomethane buffers. A cohesive bond is achieved by developing a surface layer of hydroxycarbonate apatite onto the bioactive glass through the release of ionic species from the bulk bioglass material.
Numerous applications have been found for bioactive glasses in the field of surgical and orthopedic treatments as well as in dental surgery.
A variety of bioactive glass compositions has been presented in the literature and patents. Bioactive glass compositions have been described, for instance, in European Patent 1 405 647 and European Patent Application 1 655 042, as well as in International applications WO 96/21628, WO 91/17777, and WO 91/12032.
However, the known bioactive glass compositions have a common disadvantage in that they are inherently difficult to control while being processed into products, especially when being processed into fibers in a melt-spinning process. Such troubled controllability means, for example, that the diameters of the fibers fluctuate considerably, crystallites forms into glass which leads to inhomogenity of fibers or devitrification of glass, which lowers the yield of a fiber manufacturing process. The fluctuation in fiber diameter and inhomogenity of fibers have a negative influence on further processes where the equipment and processing parameters should be fixed at least partly based on the diameter of the processed fibers. Such processes and parameters include a sintering temperature in sintering processes. Fluctuation in fiber diameter also affects e.g. the quality of the final product because thinner fibers behave in a different manner than thicker fibers. The manufacture of spherical particles and coatings is also affected by the fluctuating or non-homogenous behavior in their manufacturing processes.
In addition to the physical dimensions of the fibers or other products also some chemical features are difficult to control. For example, variation in local oxides concentration may occur, which also affects the degradation profile of the material and the ionic release profile.
Furthermore, some manufacturing related processes, for example crucible cleaning and fiber sieving, are difficult and time-consuming to be carried out.
Another drawback of the known bioactive glass compositions is that their yield in melt-spinning process is fairly low.